The exoplanet is the first ever identified with the telescope, pointing to a possible new role for Spitzer in helping to discover potentially habitable worlds, NASA said.

"We have found strong evidence for a very small, very hot and very near planet with the help of the Spitzer Space Telescope," Kevin Stevenson, lead author of the paper being published in The Astrophysical Journal, said in a prepared statement. "Identifying nearby small planets such as UCF-1.01 may one day lead to their characterization using future instruments."

The new planet was found unexpectedly in Spitzer observations while the team was studying the Neptune-size exoplanet GJ 436b, which is known to exist around the red-dwarf star GJ 436.

The astronomers noticed slight dips in the amount of infrared light streaming from the star in the Spitzer data. A review of the data showed that the dips were periodic, which suggests a second planet might be blocking out a small fraction of the star's light.

UCF-1.01's diameter would be about 5,200 miles, or two-thirds the size of Earth, and would revolve around GJ 436 at about seven times the distance of the Earth from the moon. The astronomers predict that the planet's "year" would last only 1.4 Earth days.

The planet lies far closer to its star than Mercury does to our sun, and has a surface temperature that would be more than 1,000 degrees Fahrenheit.

The astronomers believe that the planet might resemble a cratered, mostly geologically dead world like Mercury, NASA said.

Joseph Harrington, co-author of the paper, said that the extreme heat from orbiting so close to GJ 436 may have melted the exoplanet's surface, essentially leading the planet to be covered in magma.

The scientists noticed hints of a third planet orbiting the star, currently being dubbed UCF-1.02. Because knowing the mass is required to confirm a discovery, the authors of the paper are cautiously calling both celestial objects exoplanet candidates for now.

"I hope future observations will confirm these exciting results, which show Spitzer may be able to discover exoplanets as small as Mars," Michael Werner, Spitzer Project Scientist at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California, said. "Even after almost nine years in space, Spitzer's observations continue to take us in new and important scientific directions."